Various kinds of oil additive agents are put into oil used in a machine such as an engine. For example, ZnDTP which is zinc dialkyldithiophosphate is added to oil and has an antioxidant capability, a corrosion prevention capability, an anti-wear capability, and the like.
On the other hand, PTL 1 discloses use of hydrotalcite expressed by the following formula (1) as an oil additive agent.MgxAl2(OH)6+2x−2y(CO3)y.mH2O  (1)Where, in the formula (1), x and y are integral numbers satisfying 3<x<20 and 0<y<2, and m indicates an integral number. The hydrotalcite expressed by the above formula (1), according to the description of PTL 1, has characteristics of quickly reacting to an acid pollutant undesirable in the oil and indicates alkalinity value having acid value of 250 or more in the oil.
PTL 2 discloses filter media for a bypass oil filter for an internal combustion engine. According to the description of PTL 2, the filter media comprises a hydrotalcite compound expressed by the above formula (1).